Secondary air supply system for an internal combustion engine

ABSTRACT

A secondary air supply system for use with an internal combustion engine includes an air supply system comprising an air pump adapted to be intermittently operated and an air supply conduit extending from the air pump to an air manifold communicated with exhaust ports of respective engine cylinders. First and second check valves are provided in series in the air conduit so as to prevent back flow of the exhaust gas toward the air pump. The first check valve is positioned adjacent the air pump and characterized by its high blocking performance while the second check valve is characterized by its high heat-resistant and corrosion-resistant properties.

United States Patent 11 1 Yamamoto SECONDARY AIR SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE Yushi Yamamoto, Kariya, Japan Inventor:

[73] Nippondenso Co., Ltd., Kariya-shi,

Aichi-ken, Japan July 19, 1973 Assignee:

Filed:

Appl. No.:

[30] Foreign Application Priority Data July 28, 1972 Japan 47-89688 July 28, 1972 Japan 47-89697 US. Cl 60/307, 137/512}, 251/174 Int. Cl. F01n 3/10, Fl6k 15/02 Field of Search 60/293, 289, 290, 307; 417/456,458, 566; 137/512.3;251/174, 170; 418/15 References Cited UNITED STATES PATENTS 8/1920 Johnson 418/64 X 11/1927 Lockwood 417/458 10/1953 Nichols 418/84 Burrows 251/174 1 Brewer 60/293 Primary Examiner-C. J. Husar Assistant Examiner-Robert E. Garrett Attorney, Agent, or Firm Cushman, Darby & Cushman [57] ABSTRACT A secondary air supply system for use with an internal combustion engine includes an air supply system comprising an air pump adapted to be intermittently operated and an air supply conduit extending from the air pump to an air manifold communicated with exhaust ports of respective engine cylinders. First and second check valves are provided in series in the air conduit so as to prevent back flow of the exhaust gas toward the air pump. The first check valve is positioned adjacent the air pump and characterized by its high blocking performance while the second check valve is characterized by its high heat-resistant and corrosionresistant properties.

5 Claims, 8 Drawing Figures SECONDARY AIR SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air supply system for purifying the exhaust gas from an internal combustion engine and, particularly, to an improvement in secondary air supply system having means for preventing back flow of exhaust gas toward a secondary air supply source.

2. Description of Prior Art In an internal combustion engine such as an internal gasoline engine, it has been heretofore known to supply secondary air into the exhaust system of the engine downstream of the exhaust valves thereof so as to purify the exhaust gas from the engine by oxidizing the unburnt gaseous components, such as hydrocarbon and carbon monoxide contained in the exhaust gas. An air supply source for the purpose has been an air pump which is. driven by the engine or by an electric motor. In the case where the air pump is designed to be continuously operated during the operation of the engine, a check valve is provided in the secondary air supply system so as to protect the air pump from an accidental back flow of exhaust gas in the event that the operation of the air pump is discontinued due to a breakage of a drive belt for the pump or a trouble in the electric motor for the pump. In such event, the check valve is merely required to block back flow of the exhaust gas for a short time, i.e., until the drive for the air pump is repaired. The check valve is not exposed to the exhaust gas at a high temperature when the air pump is operated because secondary air flows through the valve to protect the valve from the exhaust gas. Thus, those in the art have not been required to make the elements or components of the check valve for materials which withstand extremely high temperature.

However, in aprior art secondary air supply system in which an air pump is designed to be intermittently operated by an electric motor or from an engine crank pulley through a magnet clutch and a drive belt and in which the air pump is not operated when no secondary air is needed, i.e., when the engine is' running at more than a predetermined rotational speed, there often occurs a case wherein the air pump is not in operation during the operation of the engine. In such a case, when leakage occurs in the check valve to permit back flow of the exhaust gas through the check valve to the air pump, the latter suffers from corrosion caused by harmful gaseous components and vaporized water contained in the exhaustgas with a disadvantageous result that the air pump is damaged in short time. With the secondary air supply system of the type concerned, no satisfactory result can be expected from the check valve designed for use in a secondary air supply system of the type in which the air pump is continuously operated and the check valve is required to block back flow of exhaust gas only during the repair of the drive for the air pump.

A check valve for use with a secondary air supply system in which an air pump is intermittently operated is required to be operable not only with as minimum resistance as possible against the flow of secondary air from the air pump so as to minimize the load on the pump but also with high blocking or sealing performance relative to the back flow of exhaust gas. In addition, the check valve of the class concerned is also required to have high heat-resistant and corrosionresistant properties because the valve is exposed to corrosive exhaust gas at a high temperature when the air pump is not in operation. With a secondary air supply system of so-called air injection type in which the secondary air is supplied into engine exhaust ports downstream of exhaust valves, the check valve is required to have an extremely high temperature-resistant property because, with this type of secondary air supply system, the check valve is exposed to the exhaust gas at an extremely high temperature.

One type of check valve which has been designed in an attempt to satisfy the above-discussed requirements includes valve parts made of a heat-resistant and corrosion-resistant material such as fluorinated rubber or fluorine-contained rubber. While this type of check valve is satisfactory with respect to minimized resistance of the valve parts to the flow of secondary air through the check valve and sealing or blocking performance of the valve against the exhaust gas, the check valve is not satisfactory with respect to its heatresistant property and is damaged by heat in a relatively short time. Another type of check valve includes a valve member made of a stainless steel sheet and a valve seat made of an asbestine material. The other type of check valve is satisfactory with respect to the heat-resistant property but fails to satisfactorily operate to efficiently block the back flow of exhaust gas. With the other type of the check valve, use of a higher pressure to close the valve so as to improve the sealing or blocking performance disadvantageously results in an increase in the resistance of the valve member to the flow of secondary air through the check valve. With respect to the heat-resistant property, metal is an appropriate material for the valve parts of the check valve. However, the use of valve parts of a metal encounters a problem that solid particles, such as soot, contained in the exhaust gas are deposited on the mating surface of valve member and seat with resultant leakage therebetween and corrosion of the inner components of the air pump caused by corrosive gaseous components and vaporized water contained in the exhaust gas which flows back through the check valve to the pump. Thus, no satisfactory check valve has been provided up to date for a secondary air supply system of the type in which the air pump is interruptedly operated to supply secondary air.

SUMMARY OF THE INVENTION combustion engine having an exhaust system in which means are provided for purifying the exhaust gas from the engine, said air supply system including an air pump adapted to be intermittently operated and an air conduit interconnecting said exhaust purifying means and said air pump, wherein first and second check valves are provided in series in the path of flow between said air pump and said exhaust gas purifying means so as to prevent back flow of exhaust gas through said air conduit toward said air pump, said first chect valve being characterized by its high blocking performance and positioned adjacent said air pump, said second check valve being characterized by its high heat-resistant property.

The first check valve may preferably include a first valve member made of an elastic material, a first valve seat and a first biasing means normally urging said first valve member into sealing contact with the first valve seat. The arrangement may preferably be such that the first valve member is easily opened against the first biasing means by the air supplied by the air pump when the latter is operated to thereby permit the air to pass through the first check valve. The second check valve may preferably include a second valve member made of a heat-resistant and corrosion-resistant metal, a second valve seat made of a heat-resistant and corrosionresistant material and a second biasing means normally biasing the second valve member into sealing engagement with the second valve seat. Preferably, the second valve member may have a spherical convex valve portion while the second valve seat may preferably be made of a heat-resistant and corrosion-resistant sheet metal which is resiliently deformable into intimate sealing contact with the spherical valve portion of the second valve member when the same is moved into engagement with the second valve seat. Alternatively, the second valve seat may be made of a heat-resistant and corrosion-resistant sheet material the main component of which may be asbestine or graphitic fiber.

The above and other objects, features and advantages of the present invention will be made apparent by the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagrammatical top plan view ofa reciprocating internal combustion engine equipped with a secondary air supply system according to the present invention;

FIG. 2 is an axial sectional view of a first or-seal type check valve used in the secondary air supply system shown in FIG. 1;

FIG. 3 is an axial sectional view of a second or heatresistant type check valve used in the secondary air supply system shown in FIG. 1;

FIG. 4' is an enlarged fragmentary sectional view of the engine of FIG. 1 showing an air nozzle of the system extending into the exhaust port of a cylinder of the engine;

FIG. 5 is a diagrammatical end view of a rotary engine equipped with the secondary air supply system according to the invention;

FIG. 6 is an axial sectional view of a modified heatresistant type check valve;

FIG. 7 is an enlarged fragmentary sectional view of the valve of FIG. 6 showing the valve member and valve seat thereof; and

FIG. 8 is an axial sectional view of a further modified heat-resistant type check valve with some parts thereof being cut away.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 4 of the drawings, there is shown a reciprocating internal combustion engine generally indicated by 10 and having an exhaust system including an exhaust manifold 23 and exhaust pipe. An air pump 12 is rigidly mounted on one side of the engine and is adapted to be intermittently driven through a magnet clutch 12 by pulley 13 which in turn is driven by a crank pulley, not shown, of the engine 10 through an approporiate torque transmitting means such as a V-belt not shown. The pump 1 1 has an air delivery pipe 14 connected to an end of a secondary air supply conduit 15 comprising conduit portions 150 and 1512 connected in series. A first check valve 16 is provided between the conduit portions 15a and 15b. The conduit 15 is connected at the other end to a second check valve 17 to which an air manifold 18 is connected. The air manifold 18 has a plurality of air nozzles 19 each extending into an exhaust port 20 of a cylinder 22 of the engine 10 so as to inject air into the port'20 downstream of an exhaust valve 21 for the cylinder. The exhaust port 20 is in communication with the exhaust manifold 23.

Referring to FIG. 2, the first check valve 16 comprises a housing formed of two generally cup-shaped parts 31 and 32 secured together at their large diameter ends. The housing part 31 has an outer or reduced end portion 31' to which the portion 15a of the conduit 15 is connected. Similarly, the other housing part 32 has an outer or reduced end portion 32 which is connected to the portion 15b of the conduit 15. A- substantially flat disc-like valve seat 33 is sandwiched at the marginal,

area between the inner ends of the housing parts 31 and 32. The valve seat 33 is provided with a plurality of valve openings 34 formed therein and arranged in a circumferential row. A substantially flat disc-like valve member 35 made of a corrosion-resistant elastic material such as fluorinated rubber or fluorine-contained rubber is urged against the valve seat 33 by means of a coil spring 36 having its turns normally extending substantially in a flat plane. The coil spring 36 is suspended from the valve seat 33 by means of a support 37 having a spherical convex portion and a stem portion which is connected to the valve seat. This arrangement is such that, when air is supplied from the pump 11 as shown by an arrow A in FIG. 2, the valve member 35 is easily opened from the valve seat 33 byv virtue of downward deformation of the valve member 35 against the coil spring 36 caused by the air flow A. The valve member 35 and the coil spring 36 are so designed as to have a very small resistant force against the passage of the air through the valve 16.

Referring to FIG. 3, the second check valve 17 comprises a housing formed of two housing parts 41 and 42 secured together at their large-diameter ends. The housing part 41 is generally cup-shaped and has a reduced end 41 to which other end of the conduitportion 15b is connected. The other housing part 42 has a generally drum-like shape having an outer end connected with a coupling 43 through which the valve 17 is connected to the air maniflod l9.

Disc-like support plate 44 and valve seat 46 are laminated together and sandwiched at their edge portions between the inner ends of the housing parts 41 and 42. Ths support plate 44 is advantageously made of a sheet phitic fiber. The support sheet 44 and the valve seat 46 have axially aligned central openings 45 and 47. A generally disc-like valve member 48 is normally urged against the valve seat 46 by means of a coil spring 51 extending between the valve member 48 and the outer end of the housing part 42. The valve member 48 is advantageously made of a sheet of a heat-resistant and corrosion-resistant metal such as stainless steel and is provided with a central spherical convex portion 49 and a plurality of apertures or holes 50 formed in the valve member and arranged in a circumferential row around the convex portion 49. The coil spring 51 is advantageously made of stainless steel. It will be noted that the spring 51 biases the valve member 48 upwardly so that the upper surface of the convex portion 49 is urged into sealing engagement with the peripheral edge of the opening 47 in the valve seat. The spring force of the coil spring 51 is so determined that the flow of air fed from the air pump 11, as shown by an arrow B, displaces the valve member 48 against the spring 51 and passes through the valve 17.

In operation, when the magnet clutch 12 is energized to drivingly couple the air pump 11 and the pulley 13, the pump operates to supply secondary air through the conduit portion 15a into the first check valve 16 in which the air is forced in the direction indicated by the arrow A (FIG. 2) into the openings 34 and moves the marginal area of the valve member 35 away from the valve seat 33 against the coil spring 36 so that the air passes through the first check valve 16 into the conduit portion 15b. The air is then fed into the second check valve 17 in the direction indicated by the arrow B shown in FIG. 3. In the valve 17, the air is forced through the openings 45 and 47 to move the valve member 48 away from the valve seat 46 against the spring 51 so that the air passes through the valve 17 into the air manifold 18 from which the air is distributed to the air nozzles 19 only one of which is shown in FIG, 4. The air is fed through the nozzle 19 into the exhaust port 20 in which the air is mixed with the exhaust gas at a high temperature to oxidize a quantity of unburnt gaseous components included in the exhaust gas for thereby convert the same into a substantially harmless gas.

When the gas exhausted from the engine contains relatively small amount of unburnt gaseous components and a large engine output is required as is in the case where the vehicle on whichthe engine is mounted is operated at more than a predetermined high speed, the magnet clutch 12 will be deenergized to discontinue the operation of the air pump 11. In such event, the exhaust gas at a high temperature flows from the exhaust port 20 through the air nozzles 19 and the air manifold 18 into the second check valve 17. However, because no secondary' air is supplied into the second check valve 17 in the direction of the arrow B, the valve member 48 is urged against the valve seat 46 by the coil spring 51 to close the valve 17. The exhaust gas in the check valve 17 acts on the valve member 48 in the direction opposite to the direction of the arrow B to exert an additional force on the valve member 48 with a result that the valve member is further strongly urged against the valve seat 46.

If, for some reason or accidentally, the exhaust gas should flow past the second check valve 17 through the conduit portion 15b to the first check valve 16, the exhaust gas applies a pressure, in addition to the pressure by the coil spring 36, to the deformable valve member 35 with a result that the latter is advantageously urged into sealing engagement with the valve seat 33 to close the valve opening 34 for thereby substantially completely blocking the back flow of the exhaust gas. Thus,

no exhaust gas flows to the air pump 11. It is to be understood that the exhaust gas will be at a high temperature within the second check valve 17. However, the

exhaust gas will be cooled as it flows through the conduit portion 15b and, when the exhaust gas arrives at the first check valve 15, the gas will be so cooled that the first check valve 15 is not required to have a heatresistant property. The first check valve, therefore, can have a variation in its design, i.e., the structure of the valve and the materials from which the valve parts are made. For this reason, the first check valve can be designed to have a structure which is characterized by a high sealing or blocking performance.

In the embodiment described above, the first check valve is provided in the air conduit 15. The first check valve, however, may alternatively be incorporated into the air delivery pipe 14 of the air pump 11. Moreover, the first check valve 16 may alternatively be used in combination with another valve of different kind, such as a bypass valve or relief valve.

With the described and illustrated embodiment, secondary air is injected into exhaust ports 20 of respective engine cylinders. The secondary air supply system of the present invention, however, may also be used with an engine which is equipped with another kind of exhaust gas purifying device, such as catalytic converter or afterburner, to which secondary air is supplied through a supply port either in the exhaust manifold of the engine or in the engine pipe. In such use, the first check valve will be disposed adjacent the air pump and the second check valve will be connected in series relative to the first check valve and positioned adjacent the supply port.

When it is required by a particular engine design that the air conduit 15 has an extremely small length, the conduit portion 15b'between the first and second check valves 16 and 17 may advantageously be formed of a tubing of a metal having a high heat conductivity so that the exhaust gas entering into the conduit portion 15b is rapidly cooled before the gas'reaches the first check valve.

'13 may be replaced by an electrically powered air pump of a design which is intermittently operable in accordance with the requirement for secondary air.

The secondary air supply system according to the present invention is also applicable to a rotary engine 10a as shown in FIG. 5 in which similar parts are indicated bysimilar reference numerals. The rotary engine 10a has a secondary air supply cavity 20a leading to an air nozzle'or nozzles not shown. The arrangement of the secondary air supply system shown in F IG, 5 is substantially identical with the embodiment described with reference to FIGS. 1 to 4 except that the second check valve 17 is directly communicated with the secondary air supply cavity 20a in the rotary engine 10a.

,FIG.'6 shows a modification of the second check valve. The modified second check valve is generally indicated by 17a and comprises a housing formed of two parts 41a and 42a. Those portions of the valve 17a which are similar to the corresponding portions of the check valve 17 of the described embodiment of the invention are indicated by similar reference numerals followed by a character a. The valve 17a is substantially similar to the valve 17 with the exception that housing part 410 has an annular flat portion 44a which acts as a support plate fora valve seat 46a and that the latter is made of a sheet of a heat-resistant and corrosionresistant metal. The valve seat 46a is formed therein with a central valve opening having a circumferential edge portion 47a which is deformable into intimate sealing engagement with a spherical convex portion 49a of a valve member 48a when the latter is urged against the valve seat 46a. Of course the valve member 48a can be disengaged from the valve seat 46a against the pressure by a coil spring 51a when secondary air is supplied from the air pump 11 in a direction indicated by an arrow B in FIG. 6.

The modified check valve 17a is advantageous over the check valve 17 in that the valve seat 46a of the check valve 17a is made of a heat-resistant and corrosion-resistant metal which is highly resiliently deformable at a high temperature and thus is kept in intimate sealing contact with the valve member 48a even if the valve seat 46a is subjected to a high temperature by the exhaust gas from the exhaust ports 20 of the engine. The check valve 17a provides another advantage that, because the valve member 480 is brought into face-toface contact with the valve seat edge portion 47a of small area and because the edge portion 47a is resiliently deformed at each time when the valve member 480 is moved into contact with the valve seat 46a, the check valve 17a is free from deposition, on the contact surfaces of the valve seat 46a and valve member 48a, of solid particles contained in the exhaust gas. Thus, the check valve 17a can have a prolonged operative life through which the valve member 48a can have an intimate sealing contact with the valve seat 46a without any solid particles therebetween.

As an example, the housing parts 41a and 42a of the check valve 17a have a wall thickness of '1 mm. The valve member 48a is 0.6 mm in thickness. The valve seat 460 has a thickness ranging from 0.1 to 0.2 mm.

In the case where the valve seat 460 is made of an extremely thin sheet metal, the valve seat tends to be so extremely displaced at its central portion from the support plate 44a by the supplied air that the displaced central portion is positioned close to the valve member 48a which has been opened, to disadvantageously provide an increased resistance to the flow of the secondary air through the check valve 17a. FIG. 8 shows a further modified second check valve 17a which has been designed to eliminate the disadvantageous tendency accompanied with the check valve shown in FIGS. 6 and 7.

The check valve shown in FIG. 8 is substantially similar to the check valve 17a with an exception that an additional support plate 55 is provided for a valve seat 46a so that the latter is prevented from being unduely displaced by secondary air supplied from the air pump. The additional support plate 55 has a central opening having such a size that the peripheral edge of the opening is not contacted by a convex spherical valve portion 49a of a valve member 48a when the latter is urged against a valve seat 46a. Those parts ofthe check valve 17a similar to the corresponding parts of the check valve 17a are indicated by similar reference numerals. In the structure shown in FIG. 8, the support plates 44a and 55 and the valve seat 46a are secured together in such a manner that the peripheral edge portion of the support plate 44a is curled around an outwardly extending annular flange at the top of the housing part 42a with the valve seat 46a and the additional support plate 55 being sandwiched at their outer edge portions between the support plate 44a and the annular flange. The additional support plate 55 may alternatively be secured to the valve seat 46a and the supporting plate 44a by means of spot-welding or rivetting.

What is claimed:

1. A secondary air supply system for use with an internal combustion engine having an exhaust system with means for purifying the engine exhaust gas comprising:

an intermittently operated air pump,

an air conduit interconnecting said air pump and exhaust purifying means,

a first check valve having a high blocking performance provided in said conduit adjacent said pump including a first valve member of elastic material,

a first valve seat with portions of said first valve member opposing the valve seat and a first biasing me ans normally urging said first valve member into sealing engagement with said first valve seat, the air flow from said air pump deforming said first valve member against said biasing means to permit flow and back flow of exhaust gas deforming said valve member into sealing relation with said valve seat,

a second check valve having a high heat resistance provided in said conduit adjacent said purifying means including a second valve member made of heat-resistant and corrosion-resistant metal, a second valve seat made of heat-resistant and corrosion-resistant material and a second biasing means normally urging said second valve member and sealing engagement with said second valve seat said second valve member and second valve seat having a higher heat resistance and a lower blocking performance than said first valve member and first valve seat, respectively.

2. A system as in claim 1, further including means for intermittently operating said air pump.

3. Asystem as in claim 1 wherein said first biasing means is a coil spring with its turns extending substantially in a flat plane.

4. A system as in claim 1 wherein said second valve member has a spherical valve portion which is moved 7 ond valve seat. 

1. A secondary air supply system for use with an internal combustion engine having an exhaust system with means for purifying the engine exhaust gas comprising: an intermittently operated air pump, an air conduit interconnecting said air pump and exhaust purifying means, a first check valve having a high blocking performance provided in said conduit adjacent said pump including a first valve member of elastic material, a first valve seat with portions of said first valve member opposing the valve seat and a first biasing means normally urging said first valve member into sealing engagement with said first valve seat, the air flow from said air pump deforming said first valve member against said biasing means to permit flow and back flow of exhaust gas deforming said valve member into sealing relation with said valve seat, a second check valve having a high heat resistance provided in said conduit adjacent said purifying means including a second valve member made of heat-resistant and corrosion-resistant metal, a second valve seat made of heat-resistant and corrosion-resistant material and a second biasing means normally urging said second valve member and sealing engagement with said second valve seat said second valve member and second valve seat having a higher heat resistance and a lower blocking performance than said first valve member and first valve seat, respectively.
 2. A system as in claim 1, further including means for intermittently operating said air pump.
 3. A system as in claim 1 wherein said first biasing means is a coil spring with its turns extending substantially in a flat plane.
 4. A system as in claim 1 wherein said second valve member has a spherical valve portion which is moved into and out of sealing engagement with the peripheral edge of the opening in said second valve seat.
 5. A secondary air supply system according to claim 1 wherein said second valve seat is made of a heat-resistant and corrosion-resistant sheet metal which is resiliently deformable into intimate sealing contact with said valve portion of said second valve member when the same is moved into engagement with said second valve seat. 